This invention is related to the field of water pollution and, more particularly, to a method for removing hydrocarbon pollutants and heavy metals from storm water filtration systems.
During a rainstorm, water runs off buildings, homes, sidewalks, lawns, streets, parking lots etc. of various land uses and flows into storm drains. These storm drains often conduct the storm water into a three chambered system called an oil-grit separator for removing grit (e.g. sediment, debris, etc.) and oil from the storm water. The filtered storm water may then be directed to streams or other waterways or if need be subjected to further processing.
The oil-grit separator is a filtration system made up of three concrete chambers through which the storm water must flow. The first chamber is for the removal of grit. As the storm waters flow into one side of the grit chamber, much of the sediment and debris that have been carried along sinks to the bottom of the chamber. An outlet passage is located around the middle of the opposing side of the grit chamber to permit the top portion of the storm water, absent much of the grit, to flow into a second chamber.
The second chamber is called an oil separation chamber. The storm waters flow into one side of the oil separation chamber forming a residual pool of water. On the opposing side of the chamber an L-shaped outlet passage dips below the surface level of the residual pool of water. As the storm waters join the residual pool of water in the chamber, oil washed from the streets, etc. floats to the top of the pool. The L-shaped outlet passage siphons off water below the surface of the residual pool to a third chamber and leaves the oil floating on the surface of the pool. For more severe flooding an overflow passage above the L-shaped outlet passage permits excess storm water to escape from the oil separation chamber to avoid a back-up in the system.
The third chamber allows the filtered storm water to flow on to area waterways.
Each chamber has a top access cover for cleaning and removing debris, sediment, oil and the like during routine maintenance of the oil-grit separation system. With regard to the removal of oil from the oil separation chamber, the process is both time consuming and expensive. The oil must be pumped from the chamber into a truck and removed for disposal.
Further, while statutes for regulating effluents into streams and waterways have become increasingly more stringent, budget cuts in many communities have extended the time between routine maintenance visits of these filtration systems. As a result, much of the oil in the chamber is often left for extended periods making removal and disposal of the liquid oil waste more time consuming and expensive. Also, an intervening heavy storm may push the oil in the oil separation chamber out of the overflow passage and into area waterways before routine maintenance can occur.
In addition, current oil-grit separator filtration systems have not addressed well the removal of toxic metal ions carried into the chambers by storm water effluent. These ions may also flow out of the three chambered filtration system to perhaps pollute downstream waterways.